I'd say for weight lifting, compound exercises that use multiple muscle groups (i.e., squat, bench/push up, deadlift, press, etc.). But really, for both weight training and cardio, etc., the most effective exercise is the one that you enjoy the most and will want to do rather than feeling like you have to do.

Oh God, I am so glad to hear someone else say that. I have tried, really. I still frickin hate it. I seriously would rather spend twice or three times the time doing some exercise I don't dislike as much.

Emme, to me, HIIT is all out...ALL OUT! No, 6.0 wouldn't cut it. It's more like 9.0 for 30 seconds followed by a 90 second rest, repeat for 8-20 minutes. It's a whole lot harder than it sounds. Whatever you choose to do for that 30 seconds simply has to be all out, something you can not sustain for more than 20-30 seconds. The treadmill would scare me. I'd rather sprint outside.

I have done HIIT running up and down the stairs and this is very effective. I have also done it on the elliptical or on the bike.

Emme, to me, HIIT is all out...ALL OUT! No, 6.0 wouldn't cut it. It's more like 9.0 for 30 seconds followed by a 90 second rest, repeat for 8-20 minutes. It's a whole lot harder than it sounds. Whatever you choose to do for that 30 seconds simply has to be all out, something you can not sustain for more than 20-30 seconds. The treadmill would scare me. I'd rather sprint outside.

I have done HIIT running up and down the stairs and this is very effective. I have also done it on the elliptical or on the bike.

Cool, thanks. I can only jog comfortably at 4.3 right now, so I'll see what 8 or 9 feels like to get the 20-30 second mark! I'm excited to try this!